This change adds automatic bash shell detection and integration.
Unlike our other shell integrations, bash doesn't provide a built-in
mechanism for injecting our ghostty.bash script into the new shell
environment.
Instead, we start bash in POSIX mode and use the ENV environment
variable to load our integration script, and the rest of the bash
startup sequence becomes the responsibility of our script to emulate
(along with disabling POSIX mode).
When a shell is forced, we would supply its /-prefixed executable name
to mimic a path location. The rest of the integration detection logic
assumes just a base executable name. Fix the forced names accordingly.
Also add a unit test for this "force shell" behavior.
This adds a new option to the shell integration feature set, `no-title`.
If this option is set, the shell integration will not automatically
update the window title.
